Strange bug with indexing in VSCode (failed to reproduce)

I was working with a datatable (several thousand rows and ~35 columns) inside a pylance extension in VSCode for many hours; suddenly i found out that a specific row doesn't get indexed with f expression such as
(f.Index > 1840) & (f.Index < 1870)
but gets indexed with
f.Index == 1853

the problem wasn't with the datafile, not with datatypes, and not with datatable size
i also wasn't related to the column being named 'Index'
when i relaunched vscode and read all the data back in, the problem disappeared

i assume this is some bug with memory handling or, least probable, with the integer 1853 itself